The overall objective is to learn as much as possible about the control and dynamics of hormone secretion from the pituitaries of sub-primate and lower vertebrate species, particularly the influence of hypothalamic releasing factors, and indirectly, external stimuli, and to determine the modes of action of the hypothalamic releasing factors and melanocyte stimulating hormone (MSH) in vertebrates. Other than MSH, gonadotropins are the major pituitary hormones in which we are interested, as a consequence of an involvement in studies of reproductive physiology. The immediate objectives are grouped into three areas: reproductive physiology, MSH and pigmentation, and mechanisms of hormone action. In the area of reproductive physiology, we shall investigate the endocrine basis of genetic differences in various reproductive paramters among mice selected for particular reproductive traits and we shall determine the basis for genetic differences in responsiveness to administered hormones among these lines; we shall investigate the function of the mid-pregnancy androgen surge in the mouse; and determine the hormonal changes which lead to male odor-induced pregnancy block in mice. Studies on MSH and pigmentation are directed toward the analysis of the mechanisms by which MSH affects coat color in the mouse, and the interplay of serotoninergic and dopaminergic neurons in MSH secretion in Anolis. Finally, we will use iontophoretic techniques to determine whether intracellularly administered MSH can darken frog melanophores, and whether stimulation of secretion and of protein hormone synthesis are independent actions of hypothalamic releasing factors.